This invention relates to vehicle heaters of the type which use a burner as a source of heat and, in particular, to such a heater particularly adapted for use in buses and other transit vehicles.
Conventionally vehicle interiors are heated by the engine of the vehicle. Hot coolant from the engine is circulated through a heat exchanger and one or more fans are used to circulate air heated by the heat exchanger through the interior of the vehicle. However, such heaters are not always sufficient for the heating requirements of some vehicles, such as buses and other transit vehicles which have a large interior volume. The need for another heater is increased for certain types of engines which have relatively low heat output such as four cycle diesel engines.
In addition, the vehicle engines are only an adequate source of heat after they come fully up to operating temperature and only as long as they continue to operate. Accordingly an additional source of heat may be desirable for heating the vehicle while the engine is still cold and for periods of time when the engine is shut off.
Another type of auxiliary heater is commonly employed in vehicles, typically large diesel powered vehicles, to preheat the engine prior to starting and to keep the engine warm when the vehicle is shut off. Such heaters make diesel powered vehicles significantly easier to start and reduce initial wear on various engine components including the starting system and moving components which initially may not receive adequate lubrication when the engine is cold.
At least two types of auxiliary heaters therefore are commonly available for vehicles. One is an auxiliary space heater which usually bums the engine fuel in a burner and circulates the heat to the interior by means of a fluid heated in a heat exchanger adjacent the burner. The second is a preheater to initially warm the engine or keep the engine warm while the engine is shut off. Such preheaters may also include burners operating on the engine fuel and are typically connected to the engine cooling system to initially warm the coolant or keep the coolant warm.
Auxiliary space heaters for vehicles may in fact be necessary for transit vehicles. On the other hand, preheaters may only be necessary in extremely cold climates. However, as indicated above, they may make such vehicles much easier to start, improve the life of the engine and other vehicle components and can cut emissions by allowing the engine to be shut off when not required. They also save fuel costs since the engine need not operate to provide heat. Vehicle purchasers however are often faced with the necessity of ordering two separate heaters in the vehicle, a preheater and an supplemental, fuel-fired space heater.
Another problem with the space heaters is encountered due to the continuous operation of their circulating pumps. These are typically electrically powered. The pump and motor have a limited service life. In many prior art heaters the pump circulates continuously as long as the auxiliary space heater is in operation. Eventually the pump and/or motor fail, possibly requiring the vehicle to be out of service until the components can be replaced or repaired and increasing the overall operating costs of the vehicle.
However previous attempts to prolong the life of the coolant pump by shutting the heater off have been unsuccessful. This has typically been done by shutting the heater off through external relay logic when the heater enters a standby sub-state after the coolant is heated to a preset level, typically 85.degree. C. These attempts proved to be unsuccessful because shutting the heater off in this way undermines the heater's ability to diagnose system problems through its diagnostic system, the heater's ability to automatically shut itself off when certain types of errors are encountered and the integrity of the heater data log is undermined by filling it with turn on and turn off events.
The coolant pump tends to run excessively long because the auxiliary heater tends to have a relatively light duty cycle when the engine is running because the coolant is already heated by the engine. The heater tends to therefore remains in a standby mode or sub-state for the majority of its run time with the coolant pump constantly circulating the hot coolant and with the burner off and monitoring the coolant temperature. The duty cycle of the pump can approach 100% of the time.
One problem associated with prior art preheaters is encountered with fleet operations where driver turn-over is high and driver training is typically low. Automation, in the form of a timer, can facilitate the preheating operation. However automation has not typically existed for a supplemental heater.
Another problem associated with preheaters is that they can be inadvertently left on, wasting fuel, potentially draining the battery voltage and requiring an operator to eventually turn off the heater.
A further problem associated with prior art auxiliary heaters is incompatibility with remote starting systems.
In the absence of a suitable supplemental heater, manufacturers often have employed a separate electrical heater for operation when the vehicle is running. This undesirable because it is yet another piece of equipment to install and service.
Accordingly, it is an object of the invention to provide an improved vehicle heater which can combine the functions of an engine preheater and an auxiliary space heater for the vehicle.
It is also an object of the invention to provide an improved heater for vehicles which can supplement the heat provided by the conventional vehicle heater, but does not require continuous operation of the heater's own coolant circulation pump.
It is a further object of the invention to provide an improved vehicle heater which is relatively light in weight compared with prior art vehicle heaters, particularly the total weight of a conventional engine preheater and a conventional auxiliary space heater.
It is a still further object of the invention to provide an improved vehicle heater which is simple and rugged in construction.